The present invention relates to a liquid crystal device for color display and more particularly to a liquid crystal device for color display provided with a color filter.
A liquid crystal device generally has a structure having a pair of base plates and a liquid crystal sandwiched therebetween. On a face of the base plates contacting the liquid crystal are formed elements such as electrodes and others so that the state of the liquid crystal is controlled by the elements to effect a display. A uniformly extending electrode disposed on the surface of one of the two base plates, and a plurality of electrodes in the form of small block patterns (picture elements) are formed on the surface of the other base plate.
Among the liquid crystal devices in this category, a display device using a scheme for matrix-driving a large number of picture elements as disclosed in Japanese Laid-Open Patent Application No. 17599/1975 has been watched with keen interest.
In order to make use of such a liquid crystal device, it has been proposed to provide a color filter on each electrode on one base plate having a semiconductor driving circuit thereon or on a counter electrode formed on the other base plate. A liquid crystal used for a color display comprises a large number of picture elements (as many as, for example, 480.times.640 picture elements formed by 480 scanning lines and 640 information signal lines) and thus there can be a problem that a sufficient electric field required for switching is not applied to a liquid crystal. Therefore, it is necessary to minimize the decrease in effective voltage applied to the liquid crystal. In this respect, the provision of a color filter on an electrode results in a decrease in the effective voltage applied to the liquid crystal and it is also not suitable for a display device constituted with such a large number of picture elements as described above.
A base plate provided with a semiconductor driving circuit has a sectional structure as shown in FIG. 1 and has much unevennesses as understood from the sectional view, so that it is difficult to form color filters at a rate of about 5 to 20 filters per millimeter thereon. More specifically, FIG. 1 is a schematic sectional view of a portion of a liquid crystal display device having an array of TFTs (thin film transistors) where a TFT is formed. In the figure, a letter S indicates a transparent base plate of, e.g., glass on which are successively disposed a gate electrode 1, an insulating layer 2 of, e.g., SiN:H, a semiconductor layer 3, an ohmic contact layer 4 and a source electrode. Further a drain electrode 6 is provided connected with a picture element-forming electrode 7 formed on the base plate S.
On the other hand, it has been also proposed to provide below an electrode a color filter formed by a polyvinyl alcohol film dyed with a colorant. However, such a dyed color filter can cause fading of color due to heating because an electrode film of, e.g., indium tin oxide is formed thereon by the electron beam process or sputtering process while heating the base plate provided with the color filter at 200.degree.-300.degree. C., whereby it is difficult to form a color filter with a sufficient color density.